Southern California -- this just in

The lead detective in the Mel Gibson investigation turned up "implied threats" against the actor by his ex-girlfriend and believed that a demand by her attorneys for $20 million in exchange for damaging recordings and photos merited prosecution.

The letter from Det. Rodney Wagner of the Sheriff's Department to the prosecutor who declined to file charges alleges three separate instances of extortion in e-mails to Gibson from Oksana Grigorieva and in a March 2010 meeting in which her lawyers talked with Gibson's representatives about how disclosure of the tapes and photos would "ruin" his career.

"By discussing the potential damage to Mr. Gibson's career if the 'evidence' were to be released to the public … it was my opinion, that constituted an implied threat," Wagner wrote.

Eric George, who was Grigorieva's lead attorney in the negotiations, is the son of the state's former chief justice and a campaign fund-raiser for Dist. Atty. Steve Cooley. He hosted a $500-per-person cocktail party at his Beverly Hills home in August for Cooley's unsuccessful race for state attorney general and donated $6,500 to his campaign. He declined to comment.

A spokeswoman for the district attorney's office, Jane Robison, said Cooley had no role in determining whether to bring charges in the Gibson case and downplayed Wagner's letter as "his opinion."

"He's not an attorney. Our attorneys reviewed the case and declined to file based on the evidence and the lack of evidence," Robison said.